"i am having two/three operating systems But grub loader is showing only one of them what do i do now. Please help me in this regard!!!!"
Here is the solution for these sort of questions.
Just we have to do is type a simple command.
in the terminal. It will automatically check the os in your hard drive. This will also work for the new operating systems that have added because of another hard disk connected to your cpu.
this is how it should display in the terminal.
jodiaq@jodiaq-nl:~$ sudo update-grub
[sudo] password for jodiaq:
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-3.0.0-12-generic
Found initrd image: /boot/initrd.img-3.0.0-12-generic
Found memtest86+ image: /boot/memtest86+.bin
Found Microsoft Windows XP Professional on /dev/sda1
Found Windows 7 (loader) on /dev/sdb1
We can more help on this grub editing here